The invention relates to a novel optical field-effect transistor optical signal demodulator and signal frequency downconverter and, more particularly, relates to a novel demodulator-downconverter for recovering information from a microwave modulated optical carrier signal.
Interest in developing new techniques for demodulating microwave modulated optical carrier signals has been stimulated in recent years by advances made in techniques used to impose radio frequency (RF) modulation on optical carrier signals. For example, photo-detector diodes and transistors have been used to demodulate radio frequency (RF) modulated optical signals. Light intensity sensitive field-effect transistors may have been used for this purpose.
Light intensity sensitive field-effect transistors shall be referred to hereinafter as OPFETS. Gallium arsenide (GaAs) field-effect transistors (FETs), Indium Phosphide (InP) field-effect transistors (FETs), and high electron mobility field-effect transistors (FETs) are light sensitive, hence, are OPFETS by nature but are often not used as OPFETS. Optical control of GaAs FETs used as OPFETS is known and is a technique whereby optical energy in the form of incident light influences device characteristics (permitting rf-modulated light signals to induce changes in drain-source currents flowing through a GaAs FET). However, OPFETS have not been used to their full potential.
Reported techniques for utilizing GaAs FETs to perform optical signal demodulation have not heretofore capitalized on innate OPFET gain characteristics that can be employed for local oscillator(LO) signal generation, nor have such techniques capitalized on OPFET nonlinearities for use in LO frequency multiplication and downconversion processes.
Accordingly it is desired to utilize a light-intensity sensitive FET, or OPFET (such as a GaAs FET) first, to, demodulate microwave modulated optical signals and, second, to simultaneously down-convert such signals to a lower intermediate frequency (IF) band.